1. Field of the Invention
This invention relates to poly(phenylene oxide) (hereinafter abbreviated as PPO) resin compositions and more particularly to such compositions having improved impact resistance and improved resistance to heat distortion.
2. Description of the Prior Art
PPO is a very useful thermoplastic resin which has a high heat distortion temperature and superior mechanical and electrical properties. It is used in various applications as an engineering plastics material. PPO, however, has the disadvantage of poor processability and impact resistance because of its high glass transition temperature. In order to overcome this disadvantage, several attempts have been made to improve its processability and impact resistance.
U.S. Pat. No. 3,383,435 discloses a method for improving the processability of PPO by blending a styrene polymer such as polystyrene, rubber-modified polystyrene, or a styrene-acylonitrile-butadiene terpolymer.
In Japanese Patent Publication No. 1482/1968 a method is also proposed for improving the impact resistance of PPO by blending PPO with a rubbery polymer. In practice, the above two methods are combined, that is, PPO is blended with both a styrene polymer and a rubbery polymer.
An improvement in the composition incorporating two added components is proposed in U.S. Pat. No. 4,128,602. According to this improvement, the impact strength is further increased by keeping the particle diameter of the rubbery polymer, dispersed in a matrix of PPO or a mixture of PPO and a styrene polymer, to less than 2 microns. This method, however, involves several restrictions in practice because it requires very vigorous mixing to reduce the rubbery polymer particle diameter to less than 2 microns. Alternatively, it is possible to select a specially prepared rubber-modified polystyrene in which the particle diameter of the rubbery polymer is less than 2 microns.
The requirements for PPO in the industry are increasingly stringent, and, accordingly, there is a strong demand for PPO having greatly improved flow properties (processability) and impact resistance so that it can be used for thin-walled, complex molded articles.
Hence, there is great need for a PPO composition with improved processability and impact resistance.